The present invention relates generally to optical scanning systems. More particularly, this invention relates to a scanning system having a large depth of field which is capable of focusing on and scanning a plurality of targets over a wide range of distances.
Various optical scanning systems have been developed for reading and decoding coded symbologies. Such optical scanning systems typically incorporate a light source and a light detecting means, such as a CMOS- or CCD-based image sensor. A portion of the light which is reflected from the coded symbology is detected by the image sensor and converted into an electrical signal, which is the basis for the digital image of the coded symbology that has been scanned. The digital image is then processed and decoded according to the specific type of coded symbology.
One disadvantage with prior known CMOS- and CCD-based scanning systems is that they require a mechanical focusing apparatus in order to focus the light reflected from the coded symbology onto the image sensor. Since a mechanical focusing apparatus typically operates slower than the image sensor and other electronics within the scanner, the focusing apparatus tends to be the limiting factor in the speed of operation of the scanning system. Additionally, focusing parts are subject to higher wear and maintenance requirements. Although there are scanning systems that are available which do not require a moveable focusing apparatus, these scanning systems typically have a very small depth of field.
U.S. Pat. No. 6,783,068 discloses a large depth of field camera which was developed by Accu-Sort Systems, Inc., the assignee of the present invention. This reference discloses an area array sensor used for scanning a large depth of field. An object height sensor is used to determine an object height so that the correct row of pixels is read. While the system described in U.S. Pat. No. 6,783,068 is effective for scanning a large depth of field, suitable area array sensors are currently available only at a very high cost. Further, such sensors typically transmit large quantities of information that can burden internal or external processing systems.
Accordingly, there exists a need for an efficient and inexpensive scanning system that can accurately read and decode coded symbologies over a large depth of field to focus light on an image sensor, and which can read symbologies on side-by-side objects of different heights.